I'm trying to buy a post for a potted pothos like I've seen many times, but I don't know what they're called. None of my searches have had any results.
The type I'm referring to is generally square in cross section and seems to be made of loosely compressed fibers of some sort, possibly even grape vines.
I think you are looking for a moss pole. They come in round and square shapes. Google Images Moss Pole.
Searching on Amazon for "moss pole" based on Debbie M's suggestion, I found "tree fern totem" which seemed to be closer to what I'm looking for. Searching for the latter on Google, I found that they are commonly used for orchids and a couple of references to use with pothos.